The trend towards designing and building fuel efficient, low emission vehicles has increased dramatically over the last decade, with significant emphasis being placed on the development of hybrid and all-electric vehicles. This has led, in turn, to a greater emphasis being placed on electric motors, either as the sole source of propulsion (e.g., all-electric vehicles) or as a secondary source of propulsion in a combined propulsion system (e.g., hybrid or dual electric motor vehicles).
AC induction motors are well known and are used in a variety of applications ranging from industrial to automotive. In such a motor, a magnetic field is generated by a plurality of circumferentially distributed coil windings secured within a plurality of circumferentially distributed slots in the inner periphery of the motor's stator, the coil windings being coupled to an AC power source. The magnetic field generated within the stator core causes rotation of the motor's rotor, the rotor being comprised of one or more magnetic pole pairs.
In general, the coil windings of the stator are divided into phases with the number of phases typically equaling the number of phases of the power supply. Each phase of the coil windings is then arranged into coil groups, with each coil group representing a single pole of a single phase. Each coil group is comprised of one or more individual coils or coil windings. Thus a typical winding pattern for a single phase, two-pole induction motor will include two coil groups while a three-phase, two-pole induction motor will include six coil groups. The manner in which the individual coil windings of the coil groups are arranged within the slots of the stator will determine, in part, the performance characteristics of the motor as well as its manufacturing cost. Typically, one of two winding methodologies is used, referred to as concentric winding and lap winding.
Concentric winding is probably the most common winding methodology, at least for those applications in which cost is a factor, since this methodology is easily automated and therefore relatively cost effective. In a concentric arrangement, the individual coil windings comprising each coil group are concentrically arranged about the pole center with all of the windings within a group being positioned at the same radial depth in their respective stator slots. While this approach can be automated, such an arrangement typically results in unwanted spatial harmonics in the stator winding magnetomotive force (MMF) waveform, thereby affecting motor performance.
In lap winding, the other common winding method, a coil overlapping arrangement is applied in which the configuration of each coil is substantially the same and in which one side of each coil overlaps a side of another coil. As a result of using substantially similar coils with similar winding resistances, the electrical characteristics for each phase are well balanced, thereby reducing the harmonic content in the stator winding MMF waveform. Unfortunately, while this approach yields superior motor characteristics, it does not lend itself to automation, resulting in a more costly manufacturing process.
Accordingly, what is needed is an electric motor winding arrangement that achieves the benefits of lap winding, while lending itself to automation. The present invention provides such a winding pattern and a corresponding automated manufacturing process.